Radio system



w. A. HUBER 2,627,068

RADIO SYSTEM 5 Sheets-Sheet l Jan. 27, 1953 Filed July e, 1944 W. A. HUBER RADIO SYSTEM Jan. 27, 1953 5 Sheets-Sheet 2 Filed July 6, 1944 INVENTOR.

A. HUBER WILLIAM ZONEOI ATTORNEY Jan. 27, 1953 w. A. HUBER 2,627,068

' RADIO sYsTEI/I Filed July 6, 1944 5 Sheets-Sheet 5 FIG. 5.

5| OUTPUT OF s-Ie swEEP CURRENT MOOULATOP, IN coILs Iool FIG. a.. |26- I ae.

5-2 OUTPUT OF TLFIGG 5-I9 OUTPUT OF T24.

5-3 Y VOLTAGE GROSS cON DENsER 1OO.FIG.1.

5-20 OUTPUT OF T22.

,.JJIITPIU OF INTEN- 5 4 INPUT .INTO T5. 5 2l SITI, AMPLIFIER 5-5 OUTPUT OF T 5. A MIXER |14.

5- 22 n INPUT OP T26. s-23 INPUT OF T21 II I] GRANGE MARKEFU 5-6 OUTPUT OP T e.

5-7 OUTPUT OF T1. I L 5-e INPUT INTO T9.

OUTPUT OF REcEIvEPvz 5-9 OUTPUT OF T9.

5-26 GRID SIGNAL OF T-33 51-27-|I|II||WwIW- T OUTPUT OF T33. G-IO A OUTPUT OF TII.

| IIIIIIIIIII.. .III I I.I. II OUTPUT 0F I RECEIVER #l 5 II *II OUTPUT OF T12 OURR NT w VE E A 5-29 GRID SIGNAL OF T 32 s-Iz VOLTAGE AcROss 5-3o I I OUTPUT OF T32 cONOENsER 10s. u

5-I3 OUTPUT 0F T 4- 53| INPUT SIGNA INTO T36.

5-32 OUTPUT OI= T31 I I I'II 'I I' I INPUT INTO 544 OUTPUT OF TIS. I cm2-Iso.

IN V EN TOR.

WILLIAM A. HUBER s-Ie I x OUTPUT OF T Ie. BY l/I 5-I OUTPUT oF Tal (CURRENT wAvE) MHT/j W. A. HUBER RADIO SYSTEM Jan. 27, 1953 5 Sheets-Sheetl 4 Filed July 6, 1944 INVENTOR. WILLIAM A. HUBER ffy/www SDM- orfrej W. A. HUBER RADIO SYSTEM 5 Sheets-Sheet 5 Filed July 6. 1944 IN V EN TOR. WILLIAM A. HUBER www I/ar/r/V v aux.: m. 1 L -WJ Nm. E ...jm Pl m u C mzmt: o2\ h2. m3) w Non No M NwJ L n ...mr 1 x 1 1 l l n l I l c 1 1 x I I l 4 IIL. IIJ w m @E M N2. N ma. w gf "Il A NM m2. A OMF .n u l. m2. www n; Yr m Patented Jan. 27, 1953 UNITED STATES OFFICE (Granted under Title 35, U. S. Code (1952),

sec. 266) is claims.

The invention described herein may be manufactured and used by or for the Government for governmental purposes, without the payment to me of any royalty thereon.

This invention relates to radio locators, and more particularly to radio locators using a plurality of antennas, and a method and apparatus for reproducing images of signals received by the antennas on a screen of a single oscilloscope.

When radio locators are used for determining the position of airplanes in flight, because of high flying speeds of the airplanes, it is desirable to locate their presence and position as early, and as far away, from the radio locator as practicable, and, after once locating them, to follow their course with the radio locator until they reach the locator itself, should their course of ilight be such as to coincide with the position of the radio locator. An idealized scanning beam of a system of this type should then comprise a vertically positioned rectangle with the horizontal side equal to the maximum range obtainable, such as 350 miles, and the vertical side equal to the maximum altitude attainable by the airplane, which is in the order of 40,00050,000 feet. One lower corner of such imaginary rectangle should coincide with the position of the radio locator, the radio locator being the source of the scanning beam in the system of this type.

Since the state of the known art makes it impossible to obtain such scanning beam with a single antenna array, the most practicable method of accomplishing this result consists of using two antennas, one antenna being adapted to radiate relatively low ultra-high frequency, highly directional radio signals which form a first scanning energy lobe for obtaining the desired long range, and supplementingthis long range lobe, or as it is sometimes called an early warning lobe, with an additional lobe produced bythe second antenna being adapted to radiate a higher ultra-high frequency signal for llng in that portion of the imaginary rectangle which remained unscanned by the early warning lobe. The approximate shapes of the two antenna lobe patterns accomplishing this result are illustrated in Fig. 2, lobe I being an early warning lobe pattern, and lobe I2 supplementing the early warning lobe 'by partially filling in the upper left corner of the imaginary rectangle I4.

The advantages ofsuch arrangement reside in the optimum utilization of the obtainable lobe patterns, and of the available power, which results in minimum weight of the neces-sary equipmentper unit 0i scanned area.

Since, as mentioned above, the present state of the art does not permit complete scanning of rectangle I4 with one antenna, and the sought result may be obtained only with two antennas, it becomes necessary to consider the optimum mode of mounting them on a rotating vertical shaft and a isupporting tower. Because of the relatively large size of the antenna reflectors, they represent a large resistance to wind, this resistance being at a minimum -when the two reflectors are mounted back-to-back, and the two lobes point in opposite directions, maximum wind loading being encountered when the two antennas are mounted one above the other, with both beams facing in the same direction.

The transmitting equipment in the radio locators of this type consists, as a rule, of a single modulator which keys simultaneously two transmitters, each transmitter being connected to its antenna, with the beam axes of the antennas pointing in opposite directions.

The receiving equipment in the system of this type consists of two duplexing circuits and two receivers, each receiver being connected through its duplexing circuit to the transmitting-receiving antenna. Each receiver is connected on its output side to its individual oscilloscope of a plan position type, which reproduces the received echoes on its screen along a polar coordinate system with the radio locator being located at the center of the polar coordinates. The position of targets is, therefore, indicated on the oscilloscope screen in terms of range and bearing. Except for the common modulator, the system, therefore, normally represents two complete transmittingreceiving channels. One of the reasons for using two separate Oscilloscopes, one oscilloscope being connected to each receiver, is because of the desirel tn maintain the signal-to-noise ratio as high as possible. If the two receivers were connected in parallel to a single oscilloscope, the noise level impressed on a single' oscilloscope `would be approximately twice the noise level impressed on the oscilloscope by one receiver because of the law of random distribution of the noise signals. While the noise level would be thus doubled, the level of the useful echo signals would remain equal to the output level of one receiver because the lobe patterns of the two antennas overlap only to a limited extent, and because the amplitude limiting lcharacteristics of the receivers would prevent any corresponding increase' in the amplitudes of the useful signals. Accordingly, the known radio locators using two transmitting channels and two receiving channels for locating the objects also use two separate oscilloscopes, one oscilloscope for each channel, two operators to observe the location of the echo images on two separated oscilloscope screens, and some method of coordinating the information received individually by the two operators.

'Ihe invention proposes to eliminate the need for the two indicators and two operators by displaying the signals received from both antennas and the associated receivers on a single indicator without decreasing the previously mentioned signal-to-noise ratio.

According to the invention the output circuits of the two receivers are connected to a single oscilloscope through two electronic switches which alternately block Vthe parallel connections between the two receivers and the oscilloscope so that only the output of one receiver is impressed on the oscilloscope tube at any given time. The oscilloscope itself is provided with a bi-radial sweep deflection which, like the wellknown single radial sweep deflection, known as Plane Position Indicator, or PPI, originates at the geometric center of the polar coordinates and sweeps radially at uniform radial velocity toward the periphery of the oscilloscope tube while the deflection vector is being rotated around the center at a uniform angular velocity. rhe difference between the well-known radial sweep deflection and the bi-radial sweep deflection resides in the fact that in the bi-radial deection every other succeeding radial deflection is 180 degrees out of space-phase on the screen of the oscilloscope with the deflection which preceded it, so that if, for example, radial deflection No. i extends from the center to north, the succeeding deection extends from the center to south. Because the radial deflection velocities and the rate of keying are very large as compared to the angular rotation of the antennas, the two bi-radial deflection traces appear as a straight line on the oscilloscope screen bisecting it into two semi-circles, and the echoes are reproduced in their true range and azimuth positionson both traces since one trace constantly points in the direction of the lobe axis of one antenna, and the other trace points in the direction of the lobe axis of the other antenna. Because of this resultthis type of deflection will be referred to in this specification as a bi-radial deflection. For a more detailed description of PPI systems in general, and the application of the bi-radial deflection to radio locators with a single antenna, the reader is referred to a patent application Serial No. 518,934 by W. A. Huber and M. Gindoff, led on January 20, 1944, now Patent No. 2,566,332, dated September 4, 1951.

Ity is, therefore, the principal object of this invention to provide a method and apparatus for operating a multi-antenna radio locator in connection with a single plan position indicator oscilloscope without any detrimental decrease in the signal-to-'noise ratio.

Another object of this invention is to provide a plan`position indicator connected to two receivers which alternately reproduces signals received by one receiver along one radial sweep trace, and signals received by the other receiver along the other radial sweep trace, the two traces pointing substantially in the opposite directions.

Still another objecty of this invention is to provide electronic switches ybetween the two re- .ceivers and an oscilloscope circuit, 'the switches blocking the output of one receiver and then of 4 the other receiver in synchronism with the duty cycles of said receivers.

Still another object of this invention is to provide means for synchronously operating a biradial sweep plan position indicator and a dual antenna radio locator so that the scanning results of one antenna are reproduced along one radial sweep trace and the scanning results of the other antenna are reproduced along the other radial sweep trace of said indicator.

The novel features which I believe to be characteristic of my invention are set forth with particularity in the appended claims. My invention itself, however, both as to its organization and method of operation, together with the further objects and advantages thereof, may best be understood by reference to the following description in connection with the accompanying drawings in which:

Figure 1 is a block diagram of a dual antenna radio locator connected to a bi-radial sweep oscilloscope circuit.

Figure 2 illustrates approximate shapes of the antenna lobes of the two back-to-back antennas illustrated in Fig. 1.

Figure 3 illustrates a bi-radial sweep trace pattern together with the images of the echo signals and marker signals as they appear on the screen of an oscilloscope tube.

Figure 4 illustrates the relationship between Figs. 6 and 7.

Figure 5 illustrates the oscillograrns of. the waves normally appearing in the circuits shown in Figs. Gand '7. y

Figures 6 and '7 are the schematic diagrams .of the bi-radial PPI oscilloscope, Fig. 'Y-forming la continuation of Fig. 6.

Referring now to Fig. l, a modulator lii simultaneously keys transmitters |02 and |04 which are connected to antenna arrays H36 and |08; As mentioned previously, these are the back-to-back antenna arrays with their lobe axes pointing in the diametrically opposite azimuth directions so that there is an angle of .between the axis of one lobe and the axis of the other. The antenna arrays are mounted on a vertical shaft H0 which is connected by gears H2 to a driving motor llt, and by means of a gear l I6 to a Selsyn generator I8. The drawing indicates the antenna arrays it and |66 mounted on a vertical shaft I lil so that the lobe axes of both antennas are in a' horizontal plane. ThisV may not necessarily be the case, and, in order to obtain the optimum scanning results, either one of the lobe axes may be tilted upwardly with respect to the horizontal plane. The stator winding of the Selsyn generator is connected to the stator winding of a Selsyn receiver |29. Shaft |2| of the latter is connected through adifferential gear |26 and a driving gear |22 to a driven gear |23. The deflection coils |26, .|28 of the PPI oscilloscope tube |30 are secured to gear |23 which is mounted by means of ball bearings and an appropriate collar on the neck of the oscilloscope tube. The differential gear E24 is used for the initial alignment of the electromagnetic axis of the deflection coils IZE, |23 so that the magnetic axis of the deflection coils l2@ and |28 is parallel with the axes of the antenna array beams. The Selsyns arrangement revolves the deflection coils |26, |23 in synchronism with the rotation of the antenna arrays which insures proper azimuth indications on the screen of the oscilloscope tube |30. The driving motor and the Selsyns are 5 all connected to a common source of' alternating current in a conventional manner, as indicated in the ligure.

Duplexing circuits |34 and |36 connect receivers |38 and |40 to their respective antenna arrays, and the outputs of these receivers are impressed on electronic switches |42Yand |44. The electronic switches in turn are connected to a video amplifier |46, the latter being connected y over a conductor |48 to a video channel |50. Since only one PPI oscilloscope, and 4onlyone cathode-ray beam, is used for the reproduction of the received signals on the same oscilloscope screen, the output of only one receiver may be utilized at any given time. Hence, the reason for the interposition' of the electronic switches |42 and |44 between the receivers and the video amplifier |46. The connections and the circuits of these switches will be described more fully I The output of modulator |00 is also connected 'over a conductor |53 to a range marker channel |54 which consists of an isolating amplifier |56, a range marker |58, and an isolating and inverting amplier |60. The range marker |58 comprises a short duty-cycle, freely oscillating, multivibrator the parameters of which are adjusted to produce properly spaced range marker signals 5-24, which are combined in a video channel |50 with the output of the No. and No. 2 rel ceivers, producing a composite signal 5-3I, Fig. 5. This is impressed on the cathode |6| of the cathode ray tube |30 producing intensity modulation of the cathode ray beam. The final results of such intensity modulation ofthe beam, as they appear on the screen of the 'cathode ray tube |30, are illustrated inl Fig. 3,v with the echoes appearing at 306 through 3|0, and the markers at 3|2. Sweep trace 300 to 302 is adapted to reproduce the echoes from No. re-

ceiver, while the sweep trace 3D0-to 304 may be modulated to reproduce the echoes from No. 2 receiver. The entire range marker channel may be omitted altogether if it is' preferable to use a properly engraved, transparent scale superimposed over the oscilloscope screen. Since the full ranges of the two exploratory channels, in this case, are-unequal, it'ispreferable to use a rangemarker channel because-the two different range scales',"superimposed over the same screen, would tend to be confusing.

Modulator is also connected over a conductor |6| to a pulse frequency divider |62, preferably consisting of an Eccles Jordan multivibrator circuit which generates a series ci rectangular waves -2,- Fig. 5, and, in effect, aids, in connection with the additional circuits connected to it, to direct one modulator pulse to one sweep voltage channel, and another succeeding modulator pulse tov the other sweep voltage channel. To accomplish this result, the pulses `forming the rectangular Wave 5-2 appearing in the output of the divider |62- are impressed in parallel on two diierentiatin'g networks', separators and shapers |64, |66 where they are transformed into two series of rectangular pulses 5-6 and 5|4, the iirst series of pulses being derived from the even numbered modulator' pulses, and the second series from the odd numbered modulator pulses. These pulses are also illustratedin Fig. 5 and bear the same numerals in that gure. Pulse 5|4 is used for controlling a delayed multivibrator |68 as well as a saw-tooth oscillator, an amplifier and a clamper connected to it. Pulse 5-6 controls a precision delayed multivibrator |10 and a differentiating network connected in the output of the latter, the output of the network controlling the circuits included in a block |12 which, except for some diiierence due to circuit constants, is identical to that of the circuits included in the block |68. Two sawtooth current waves 5-|| and 5|1 appearing in the output of the ampliers, which represent theoutput stages of the two sweep voltage channels, are impressed on the rotating electromagnetic deflection coils |26 and |28 where they produce the radial deflection of the cathode-ray beam alternately in the diametrically opposite directions from an approximate geometric center of the cathode ray tube screen.

It has been previously mentioned that the defiection coils |26 and |28 are rotated in synchronism with the antennaarrays |60 and |06; although the antennas as well as the deflection coils are rotated at uniform angular velocity, and advance continuously at a uniform rate, this angular velocity is so low as compared to the outward radial travel velocity of the cathode ray beam, and the angle through which the coils advance during each sweep is so infinitesimal, that the No. and No. 2 sweep traces appear as a substantially straight line on the oscilloscope screen as illustrated in Fig. 3 where the two traces form a straight line 302-300-|304, bisecting the oscilloscope screen.

In order to block the cathode ray beam on its return trips and between deflections, the blockage in the latter case being necessary when the keying frequency is so low that there are idle periods between deflections, a positive bias is applied to cathode |6| through a potentiometer arm |65 connected to s, bleeder resistor |63. To overcome this bias during the linear portions of the sweep deflections, the outputs of the multivibrators |68 and |12 are connected to an intensity amplier andmixer |14; its output is connected to an intensity grid |16 througha potentiometer |18. Since the positive rectangular waves 5-2I are impressed on the intensity grid |16 at the very same time that the linear portions of the saw-tooth waves 5| and 5| 1 are impressed on the electromagnetic deflection coils |26 and |28, only the echoes which coincide in time with the vlinear portionspfthe' Vsaw-tooth wavesV can appear on the Oscilloscope screen.

summarizing briefly the operation of the radio locator disclosed in Fig. l, the antenna arrays |06 and |68 `and the deflection Icoils 26 and |28 are rotated at the same angular velocity. Two transmitters are keyed simultaneously by one modulator and two exploratory pulses are transmitted at the very same time by the antennas in the diametrically opposite directions. The relationship of the rotational speeds of the antennas and of `the'deflection coils, and the rate` of keying of the transmittersis such that the biradial sweep-tracesforma substantially straight line on the oscilloscope screen; lThe received signals are impressed ori-'two receivers, and -electronic switches key the outputs of the receivers so that only the output of one receiver is impressed on the oscilloscope circuit at any' given time. The electronic switches areV operated in synchronism withthe sweep channels so that either one or the other receiver impresses its signals on the oscilloscope circuit during the linear portions of the saw-tooth waves. Accordingly, the signa-ls from N0. lI receiver are reproduced along one radial sweep trace and the signals from the other receiver are reproduced along the opposite trace, the two traces constantly pointing in the directions of the respective lobe axes Aso that true azimuth location of the objects is reproduced on the oscilloscope screen. No alternate llzeyi'ng of the transmitters is used in this system since it is presumed that the auxiliary Oscilloscopes, which arey often. used withV systems of this type, are connected to the No. I and No. 2 receivers thus requiring continuous operation of the two transmitting-receiving channels. Another arrangement, permitting alternate keying ofthe transmitters is illustrated in the joint application of W. A. Huber and N. T. Volsk, Serial Number 571,642 tiled January 6, 1945.

Reference is nowmade to Figs. 6v and 7, the relationship of which with respect to eachother is illustrated in Fig. 4, Fig. 7 being a continuation of the circuits shown in Fig. 6. Figs. 6 and 7 are the schematic diagrams of the Ici-radial' oscilloscope sweep circuit and of the video channels, including the electroni-c switches for alternately keying the video channels, the transmitter-receiver combinations not appearing in these iigures since it per se does not form a part of this invention. 'I'he disposition of the various elements in these gures, which correspond to the same elements also shown in a block form in Fig. 1, is as follows: the range marker channel |54 appears in the upper left corner of Fig. 6, the pulse frequency dividing multivibrator |62 is in the upper right corner of Fig. 6, and the y6; in Fig. 7 No. I sweep channel appears at the top, No. 2 sweep channel at the bottom, and the intensity amplier and mixer I'Il is in the central portion of Fig. 7V and between the No. I and No. 2 sweep channels. The oscilloscope tube |30 is in the upper right corner of Fig. '7.

Proceeding first with the description of the circuits of the No. I and No. 2 sweep channels, these channels begin with a conductor I6I (top of Fig. 6) which impresses the positive voltage signals I, generated by modulator IDB, on the control grids of ti'iod'es T-I and T-2, which comprise an Eccles Jordan multivibrator circuit. This type of multivibrator circuit is well known in the art, and needs no detailed description. As mentioned previously in connection with Fig. 1, it has two degrees of stability, one tube being fully conductive while the other is nonconductive, and vice versa, the conductivity of the tubes being controlled either by positive or negative voltage pulses impressed in parallel on the control grids of the two tubes. Once put into one state of stability, the circuit remains in this position indenitely until it is put into the other state of stability by the succeeding control pulse 5 I. The voltage signal appearing in the plate of tube T-l is a rectangular wave 5 2, the duradenser-resistance combinations 104, and 10.3 105. Her-e it is transformed into a series of positive and negative pulses 5 3 and 5 I2 respectively, which are impressed on the plate and `cathode of diodes T-3 and T-4 respectively. Diode T-By is rendered conductive by the positive pulses, and diode T-4 is rendered conductive by the negative pulses. The voltage signal impressed on the control grid of a triode T5 is illustrated at 5 4. Since the control grid Vof T-5 is coupled to a cathode resistor 10| of diode T-3, the signals Vimpressed on this grid have positive polarity, the negative signals having been by-passed to ground by resistance 104 without producing any voltage signal in the cathode resistor 1,0I. Diode T.-3 represents the beginning of No. 2 sweep channel, and the circuits of this channel will be described irst; it will then be followed by the description of No. I sweep chan- Triodes 'll-5 and T-G are two shaping ampliers which transform signal 5 4 impressed on the control grid of vT'5 into a rectangular pulse 5 6; Triode T-'5 is overdriven by signal 5 4 so that an approximately rectangular pulse 5 5 appears in, its output. Triode T-G is normally conductive and is overdriven in a negative drection by the negative pulse 5 5 so lthat its output r-epresents a substantially rectangular pulse 5 6. This is impressed on a potentiometer 104 which is connected to the control grid of a triode T-1 through a coupling condenser 10B.

Triodes T-1 and T- represent a precision delayed multi-vibrator circuit which is used for generating a rectangular wave 5-1 of adjustable width. This multivibrator comprises a twin triode biased multivibrator, the width of the output pulse of which is a linear function of the grid bias impressed on the grid. of the iirst triode T-1 by a biasing battery T09 and a potentiometer 108 through a` grid resistor H0. Potentiometer 10E comprises a source of variable biasing potential which is used for controlling the width of the rectangular wave 5 1 appearing in the output circuit of triode` 'Il-1. The common cathode of the triodes is connected to ground over a cathode resistor 1I'2 and. the plates are connected to a positive source of' potential 1I4 over resistances 'II6 and 1I8. Theegri'dof triode T-S is coupled to the plate of triode T1 over a condenser 126, and to theA positive source of potential 1I4 over a resistance 122. Condenser 12I is a bly-pass to ground condenser.

The operation of this multivibrator circuit is as follows normally, the secondl triode T- is conductive since its grid is held at approximately the cathode potential by the grid current through the large grid resistance 122. The voltage drop through the common cathode resistance 1I2 is sufficient to make the cathode positive with respect to the grid of the rst triode `T-1 which is, therefore, nonconductive. Condenser is charged to a voltage equal to a potential difference between the platel of T-I- andthe grid of 'll-8 because of the small grid current drawn by T-8. A positive trigger voltage 5 6 is applied through a small coupling condenser 106 to the grid of T-l. The time constant ofthe grid circuit of T-1 is made very small (in the order of one quarter of one microseconds), so that only high frequency components of the trigger signal passes into the grid circuit. A diode may be used between T-'G and T-T to insure that the voltage applied to theI grid is positive. A positive trigger of about 0.2 microsecond results and T-1 thereby becomes conductive. The plate voltage tial.

of T-I drops, and through condenser 120 the grid of T-8 is driven below the new cathode poten- The cathode potential falls immediately after the trigger pulse to a value which is determined by the grid bias impressed on the grid of T-1 by potentiometer 108. In this condition T-1 is conducting and T-8 is nonconducting.

As the grid of T-8 is no longer conducting, condenser 120 discharges through the resistances 122 and 1I6, and the grid potential of T-8 rises to the point at which T-8 begins to conduct. At this point T-1 is cut on' and the multivibrator returns to the quiescent condition. The change occurs very rapidly and in a regenerating fashion. With the beginning of the current in T-8 the cathode potential rises to cut oil` T-1, which in turn raises the grid potential of T-8 through condenser 128 increasing the current in T-B.

The pulse width can be altered by changing the values of the resistance 122, condenser 120, resistance 1I2, or the grid potential impressed on the grid of T-1 by potentiometer resistance 108. The variation of the grid potential is actually the most convenient method of controlling the pulse width. Its principal effect occurs in changing the cathode potential when T-1 is conducting and thereby changing the amount condenser 120 must discharge before T-8 begins to conduct. It also varies the plate voltage of T-1 when the latter is conducting. It may be shown experimentally as well as theoretically that this,

together with the curvature of the grid-plate characteristic of T-1, results in a high degree of compensation of the inherently non-linear relationship between the voltage and discharge time of condenser 120. Because of the highly accurate linear relationship between the pulse width and the grid voltage, the multivibrator T-1 T8 is here referred to as a precision delayed multivibrator. The highly accurate linear relationship between the pulse width or the duration of the duty cycle of this multivibrator and the grid voltage is utilized for changing the time of occurrence of the saw-tooth wave generated by the No. 2 sweep channel and for determining the range up to that point at which the early warning range begins. Therefore, the range reading in this case consists of the range reading as it appears on the calibrated scale oi potentiometer 108, plus the reading of the early warning sweep. Moreover, the calibrated potentiometer 108 is used for quickly selecting the desired starting point. of the early warning range for its reproduction on the Vernier range. Potentiometer 108 may also be used for determining at once the entire range of any desired echo (within certain limits which will be discussed later in connection with the operation of the system) by positioning its image on the oscilloscope screen in line with a reference circle 328, Fig. 3 engraved on a scale dial superimposed upon the oscilloscope screen.

The rectangular wave 5-1 is impressed on a I differentiating network 124-126, which transforms it into a series of positive and negative pulses 5 8. These are impressed on the control grid of the first tube of a second delayed multivibrator circuit consisting of triodes T-9 and T-I; the connections and the functioning of which are identical to those of the precision delayed multivibrator T1 T8 with two exceptions: the biasing potential impressed on the control grid of T-S remains fixed while the time constant of a resistance-condenser combination 12S-13D is made adjustable so that in this multivibrator it is the parameter of the second control grid that is made variable for varying the width of the rectangular wave 5 9 appearing in its output. It is the duration of this rectangular wave that determines the duration of the linear portion of the No. 2 sweep. Therefore, multivibrator T9 TI Il circuit is adjusted so that the duration of the rectangular wave 5 3 corresponds to the desired range span of the early warning sweep. Normally once this adjustment has been made it remains fixed.

The rectangular wave 5 9 is impressed on the control grid of a triode T-II which comprises a single-ended saw-tooth oscillator of the No. 2 sweep channel. The control grid of T-II is connected to the bleeder resistor 1 I 4 which impresses positive potential on this grid through a grid resistor 132; therefore, T-I I is normally fully conductive so that a sweep generating condenser 134 is normally kept in a substantially discharged condition. This condenser is connected across the output of T-II in series with a parallel resistance-capacity network 138 139. The plate of T-I I is connected to a positive source of potential 1I4 over a plate resistor 13G and an isolating resistor 142, the latter being shunted to ground by ya filtering condenser 144. When the negative rectangular wave 5 9 is impressed on the control grid of T-I I, it renders this grid negative and T-II nonconductive. The voltage across condenser 134, which was quite low because of the high IR drop in the plate resistors 136 and 142 as long as T-II remained fully conductive, now instantaneously jumps up to an intermediate positive potenti-al due to the instantaneous IR, drop appearing across resistor 139. After reaching this initial instantaneous potential, condenser 134 begins to charge resulting in a linear portion of the sweep wave 5 I0. This initial abrupt start of the voltage sweep wave E I is necessary because it is later impressed on the rotating yoke coils I26 I28 which have considerable inductance, and it is only the voltage of this form that can produce a linear current wave 5 II in these coils and a linear change in the beam defiecting flux in the oscilloscope tube. Variable condenser 138 is provided for adjusting the initial instantaneous voltage wave front of the voltage wave 5 I0; the smaller this condenser is, the more instantaneous is the initial rise of the voltage wave. Resistor 136 may be a variable resistor so that proper initial voltage rise may be obtained at condenser 13 9. Thus, in order to produce eventually the linear sweep by means of the rotating coils I26 I28. the voltage wave 5 I0 may need some adjustment by means of condenser 138 and resistance 139 until the desired linear current saw-tooth wave 5 II is obtained. While condenser 138, when varied, may make the sudden voltage rise either more or less abrupt, variation of resistance 139 will make the amplitude of this rise either higher or lower. The voltag-e wave 5 Iil is applied to the grid of a beam power tube T-I 2 which, after linear amplication of this wave, impresses it on the rotating coils IZB-|28 over a conductor 148. The cathodeplate circuit of this tube is as follows: cathode 143, conductor 148, coils I26 I28, ground 155, a grounded source of potential 1I4, and a plate 15 I. The A. C. grid circuit of this tube is through a condenser 152, resistance 136, condenser 144, grounded bus 155, ground 150, coils I26 I 28, conductor 148 and cathode 143.

In order to stabilize the central position of the beam on the cathode-ray oscilloscope, the conis Abelow the ground potential.

acerbes trol grid of TL-IZ is also connected to a clamper circuit consisting of tubes T-I3 and Il-I4 which act, when conductive, as two variable uni-directional resistances connecting control grid 154 to a grounded tap 158 through a bleeder resistor 156. These tubes clamp, or hold, the grid potential of the power -amplier tube T-l 2 at a steady, 'xed potential which renders T-IZ nonconductive when no saw-tooth wave is impressed upon it. It is essential than T-IZ always returns to and retains exactly the same, constant cut-oir` potential between the saw-tooth waves for two reasons: iirst this tube should remain continuously nonconductive during its inactive period so th-at it` does not interfere with the saw-tooth wave 5-i1 impressed on thecoils by the second power amplifier T-Zi of lthe No. l sweep channel; and, second,V TI2 must always return to exactly the same cut-off point on its transconductance curve so 'that when the neXt saw-tooth wave is impressed upon it, it will start amplifying this wave from that xed cut-oir point thus impressing on the deflection coils current saw-tooth waves of the continuously equal amplitudes. That this 4must be the case is not difficult to understand, since it has been previously stated that the accuracy of all range determinations depends upon the fact lthat the sweep always starts from the zero range center on its outward radial journey, and that the range is determined by measuring radial distance from this -zero range center. Any lack of stability-in the circuits of T-l2 would immediately result in a wandering zero range poi-nt and inaccurate range determinations.

Proceeding now with the description of connections of the clamper circuit, the clamper tubes T43 and T-l 4 are connected to a separate source of potential shown as a bleeder resistor 156, an intermediate point 158 of which is connected to ground. The resistor is by-passed to ground by condensers 163 and 165. The plate of T-I3 is connected to the positive end of resistor 158, while the cathode ofV T'-l4 makes a potentiometer type Vconnection with the same resistor through a potentiometer arm 16| connected to a point which y The potentiometer arm 16| and the ground tap- 158 are so positioned onresistor 156 that suiciently negative potential is impressed on the control grid of the power amplifier tube T-I2 so as to normally render T-IVZ 'nonconductive The fact that the positions of the potentiometer arm 16| and of tap 158v determine the biasing potential normally impressed on the control grid of '1l-i2 will become more apparent from the description of the functioning cycle of the clamper circuit. The control grids of T-l3 and T-M are connected in parallel tov a coupling condenser 160 and toa grid-resistor 151, the other end of which is connected to the positiv-e end of resistor E. Normally T-l3 and T-I 4 are both conductive because of the full plate potential initially appearing on their control grids. When this is the case, T'-l4 becomes conductive and current flows from its cathode to its control grid and the plate. This current at once'enables '2F-'I3 to become conductive 'so that the'twctubes conduct a series current from the cathode of T-lfl to the plate of tube T43. The grid current carried by the control `grid of T-M produces an IR'drop in the grid rethe control grid is not very far removed from the ground potential, the cathode of T-Ii is below the ground potential thus making this current possible; the second current is from the cathode to its plate, and it is this current that mainly determines the potential between ground and the control grid of 'll-2 at this instant. By adjusting the positions of the potentiometer arm 1S! and ground tap 153 on the bleeder resistor 156, the conductivity of T-M may be controlled thus controlling the potential appearing on the control grid of r1"-I2. Referring again to the current iiowing in series through 'the two tubes from the cathode of T-M to the plate of T- i3, it is apparent that the potential impressed on this series circuit by resistor 15G will divide itself across the cathode-to-plate impedances of the twotubes. Because of different grid-to-cathode voltages, these impedances will not be equal, and, therefore, the potential drop across T-lll will be lower than the potential drop across T-l 3. These grids are always at the same potential to ground, while the cathode of T-lli is always at a much lower potential to ground than the cathode of T`I3; therefore, 'ILM will be always more conductive than T-I3, the excess Vcurrent carried by T-M being diverted to the control grid of 'l1-id. The entire circuit is so adjusted by adjusting the potentiometer arm 16| and ground tap 153 that the voltage drop across vT-lfi is considerably lower than the same voltage drop across T--l3, and the grid of 'IJ-I2 is at its cut-ofi potential when T-l3 and 'IL-i4 are in their normal conductive state.

If, at this instant, `any interference signals appear across the coupling condenser 152, they are immediately discharged either across T'l3 or T-I4 so that the control grid of 'Il-i12 retains its constant potential with respect to ground. When the signalsV impressed 'by the coupling condenser 152 are of negative polarity, they decrease the conductivity of 'ILM 'and increase the conductivity of T-I3 in proportion to the disturbance created by the condenser and this change in the conductivities of the clamper tubes 4immediately restores theY potential of the control gril of 'Il-l2 to its normal value. The same is true when the interference potentials are of positive sign, except that in this case T-Hi becomes more conductive and T-l3 less conductive. The control grids of T43 and T-I'lt are connected tothe output of T`-9, the first tube of the multivibrator, over a coupling-condenser 16E) which periodically impresses upon these grids the negative rectangular wave 5--9 rendering these grids negative with respect to the cathodes. The alternating current circuit of condenser 1%0 is: resistor 151, grounded condenser 165, grounded bus 155, condenser 12s, plate resistor 13|, and condenser 16o. When the negative rectangular wave is impressed across the gridv resistor 151, and T-`l3 and T-Ul become nonconductive, they are transformed into high impedance devices, and, therefore, T-l2 can now amplify the sweep wave impressed upon its control grid yat this instant by the sweep generator T-I I.

Referring now to No. l sweep channel, it begins with a differentiating Vnetwork 1&3-165 connected to a diode T-li. This diode is rendered conductive by the negative signals so that its plate output appears as a negative signal 5-I3. This signal overdrives a normally conductive shaping triode T-I 5 in the negative direction resulting in a rectangular pulse 5-l4. It is impressed on a delayed multivibrator consisting of 13 triodes T`I S, T-I 1 which correspond to the same type of multivibrator T'9, T-III in the No. 2 sweep channel. A rectangular wave |5 appearing in the plate circuit of triode T-IS is impressed on the control grid of a saw-tooth generator T-IS and clamper tubes T|9 and T2|l. The clamper tubes are connected to the control grid of a power ampliiier T-2| which is connected to the coils |26, |28. The functioning as well as the connections of these elements is identical to those in the No. 2 channel, and therefore needs no additional description.

Comparing the connections and the elements in the No. I and No. 2 sweep channels, one may readily see that there is no precision delayed multivibrator in the No. I sweep channel while there is one in the No. 2 channel. Accordingly, the No. I sweep channel, and especially itsmultivibrator T| S-T-I1, is so adjusted that the generated sweep trace corresponds to the maximum range of the upper lobe I2, Fig. 2, and its duration as well as its position with respect to the transmitted signal remain xed. Accordingly, all signals received by means of this lobe are reproduced on this sweep. In the No. 2 sweep channel, the duration of the saw-tooth wave 5II also remains fixed, and its time of occurrence with respect to the transmitted signals is adjusted so as to reproduce the outlying portion of the range, which is beyond the range of lobe I2. Accordingly, only the early warning portion of lobe IS f appears on the No. 2 sweep.

To avoid any range gap between the two sweeps, the precision del-ay multivibrator T-1- T-8 is adjusted so as tomake the initial portion of the saw-tooth wave 5I I include the extreme range portion of the saw-tooth wave 5-|1. The keying rate of the transmitters must be adjusted so as to allow the saw-tooth wave 5| I to reach its zero amplitude point before there is an appearance of the saw-tooth wave 5-I1. This is illustrated at 5-I 8 in Fig. 5.

Proceeding now with the description of the range marker channel |54, the schematic of which is shown in the upper left corner of Fig. 6, the keying pulse from the line pulse modulator ISS is impressed over conductor |53 on an isolating amplifier T-ZS which is so biased that it linearly ampliiies the rectangular pulses 5| impressed upon it by the modulator. Triodes T-21'and 'IL-28 comprise a short duty cycle, selfoscillating multivibrator, the frequency of which is adjusted by means of a variable cathode resistor S30 so that it generates a series of uniformly spaced rectangular pulses 5--24. Pulses 5-23 are impressed on the control grid of triode T21, thus time-phase synchronizing the oscillations of the multivibrator with the starting periods of the saw-tooth wave 5-|1, and the appearance of the exploratory pulses 5| of the cathode ISI of the cathode ray tube |30. This synchronization of `the multivibrator circuit insures accurate location of the zero markers and all other range markers on the oscilloscope screen. The time interval between the duty cycles of this multivibrator is so chosen that it represents some convenient range distance on the screen of the range oscilloscope. For example, if the full range of the system is 300 miles, the time interval between the duty cycles may be adjusted to produce 10 or 20 mile range markers SI2, Fig. 3, on the oscilloscope screen. The output of the multivibrator is impressed through an isolating and inverting amplifier T-29 and a conductor 63| on :the control grid of a mixer 14 tube T-BS in the Video amplifier and mixer 'channel |50.

The video channel begins in Fig. 6 with two conductors, |39 and |4I, which connect the output circuits of the No. I and No. 2 receivers to to two tetrodes T-30 and T-3I. These negatively biased tetrodes act as linear ampliiiers of the positive video signals impressed upon them by the receivers. Choke coils S00 and 66| are inserted in the plate circuits of tubes T-30, T-3I, T-32, T-33, T-3S, T31 and the cathodes of T-32 and T-33 to effect high frequency compensation. Triodes T-32 and T-33 act as nonadditive electronic switches in the two parallel video channels. The grids of the triodes T-32 and T-33 are directly connected to the plates of triodes T-34 and T-35 respectively. The grids of the normally conductive triodes T-3'I and T-35 are connected over conductors |50 and |52 to the outputs of the multivibrator tubes T-I6 and T-9 shown in Fig. '7, which impress on the grids of T-34 and T-35 negative rectangular voltage waves 5|5 and 5--9 respectively. Thus T-34 and T-35 are rendered alternately nonconductive for the periods of time which are equal to the duration of the duty cycles of the No. I and No. 2 sweep channels. The circuit of the control grid of T-34 is as follows: conductor |50, grid resistor 180, and a grounded bleeder resistor 19|. With no rectangular wave 5|5 impressed on the grid of T-34, because of the positive potential impressed upon it by the bleeder resistor 19|, T-34 is fully conductive. Since the grid of T-32 is directly connected to the plate of T-34, it is approximately at ground potential when T-34 is conductive because of the IR drop in the plate resistor S02, and is considerably below the full positive potential impressed on the cathode of T-32 over a resistor 603, inductance 62|, conductor S61, and bleeder resistor S04. This renders T-32 nonconductive even when there are signals impressed on the cathode of T32 by the video amplifier T-3II through the coupling condenser SI2, inductance S2|, and resistance 603. When the negative rectangular wave 5-| 5 renders the grid of T-34 negative, T-34 is rendered nonconductive, and the grid of T-32 assumes a potential equal to the potential of the cathode, full positive potential being now impressed upon both of them by the bleeder resistor S04. If at this time any negative signals are impressed on the cathode of T-32 by T-3I) over condenser SI2, T-32 is made to act as a diode and is thus rendered conductive, as illustrated at 5-21 in Fig. 5. The connection between the plate and the cathode of T-32 is over inductance S25, resistors S20 and S06, the cathode resistor 603 and inductance 62|. The video frequency circuit of condenser SI2 is as follows: the plate of T-30, condenser SI2, cathode inductance 62|, resistor S63, grounded condensers 622 and 6| and the cathode of T-3S. The output of T-3'2 is connected through a condenser 608 and a resistance-condenser combination S09, SIS to the control grid of a mixer tube T-3S which is normally fully conductive. Resistances SIS and 6 I3 are used for isolating as much as possible the triodes T-32, T-33 and 'li-29 from each other so that any variation in the potential of the junction point SI5 would not have any feed-back action on the triodes T-32 and T-33.

The advantage of the electronic switch resides in the fact that the keying signals impressed on the grid of T-32 do not disturb the normally nonconductive state of T-32 since the cathode and the plate of T-32 are connected to the same source of positive potential lli, and only the negative signals impressed on its cathode, while the grid potential is made positive, can make this tube conductive As a consequence, only the desired signals, impressed on the cathode of T-32 by T-S through the coupling condenser SI2, can appear in the output of T-32. It is impossible to obtain such results when a multigrid mixer tube or a pentode is used as an electronic switch with one .grid connected to the signals and the other grid to the keying pulses since in such a case altering of potential on one grid by means of the keying pulses immediately alters the conductivity of the tube with the result that the keying pulses themselves, as well as the desired signals, appear in the output of the tube. Moreover, there is a modulation of the keying pulses by the desired signals, higher percentage of the keying pulses appearing in the output when the amplitude of the desired signals is high, and vice versa.

The video circuits between the output of receiver No. 2 and the mixer stage T-, which include a negatively biased amplifier tube T-SI, a keying triode '2F-35 and a triode T-.33 blocking the signals from the receiver No. 2, correspond to the same respective elements T-SQ, T 34 and T-32 in the No. I receiving channel. The action of these tubes is, therefore, identical to the action of the respective elements in the No. I channel, i. e. they impress the video signals on the control grid of the mixer stage T-SS during the duty cycle of the No. 2 receiver, as shown at -2il through 5-.36 in Fig. 5.

The functioning of the electronic switching circuit may be brielly summarized then as follows: because of the difference in the antennae lobe patterns and the difference in the echoes received by the two antennae, it is necessary to separate the outputs of the two receivers in the oscilloscope, and reproduce all echo signals received by the No. I receiver on the No. I sweep and exclude all signals that may be received at this time by the No. 2 receiver. This is accomplished by blocking T-33 duringthe duty cycle of the No. l receiver. Conversely, when the output of the No. 2 receiver must be impressed on the cathode of the cathode-ray tube, the output of the No. l receiver must be blocked, and this is accomplished by blocking T-32 during the duty cycle of the No. 2 receiver.

A normally fully conductive pentode T-S thus receives the video signals rst from one receiver and then from the other, and it also continuously receives the marker signals from the range marker channel. The polarity of all these signals is nega-tive, as shown at 5-31 in Fig. 5, and, therefore, T-Bi impresses positive signals on the control grid of a normally nonconductive amplifier pentode T-S'i. Here the video and marker signals are amplified and are impressed on` a coupling condenser Ele and a conductor BIB as negative pulses 5-32 thus, depressing the potential of cathode iti, Fig. 7, of the cathode-ray tube E35. A D. C. diode restorer T-38 is connected between conductor GIS and ground through a coupling condenser SIS.. If any positive signals appear on the lconductor EIS because of the capacitive nature of the circuits used for coupling the output stage of the video amplifier T-3'I to cathode Iiil, they are shorted to ground by the D. C. restorer T-38 thus stabilizing the normal positive biasing potential impressed on 16 cathode lill 'by the `bleeder resistor |63 over con` ductor 623 and resistaneZS.

The video and the marker signals 5-32 produce a series of bright marker dots 3I2 or bright echo arcs 30G-3H] on the screen of the oscilloscope as illustrated in Fig. 3.

It has been previously mentioned in this specification ythat the rotational speed of the antenna arrays |05, |68 is, as a rule, quite low because of their Weight, rotational speeds inthe order of one or two R. P. M. being the customary speeds ordinarily encountered in actual practice. However, higher rotational speeds may be used occasionally when an unusually high rate of scanning of the surrounding space is imperative, and, when this is the case, the rotational speeds may rise to as high a value as 20 R. P. M. When the antenna rotational speeds are in the order of one to two R. P. M. and the keying rate of vthe transmitters IGZ and U14 is in the order of 300 Vcycles per second, very satisfactory signal reproductions are obtained ,on the oscilloscope screen without any overlapping of the two sectors when the retentivity of the screen is in the order of P-'i screen, RMA code. However, as the rotational speed of the antennas is increased above two Ri. P. M. with the keying rate remaining constant, because of the relatively high retentivity of the P-'I screen, considerable glow may be retained on the screen at the trailing ends of the sectors up to the time of appearance of the following sectors, resulting in a simultaneous reproduction of signals by the two channels over the same screen sectors. This would obviously result in the confusion of the images on the oscilloscope screen. To avoid this confusion a three-position switch 182 is provided, the rotating arm of which is connected to a grounded bus 181i, terminals No. 2 and No. 3 of Ywhich are connected to the outputs of the shaping amplifiers 'll-6 and T-I5 respectively. The shaping amplier T-,B is connected to the No. 2 terminal by means of a conductor 180. When switch 182 makes contact with terminal No. I, No. I as well as No. 2 sweep channels are operated in the usual manner, since this is the open position of the switch. When the switch is turned to terminal No. 2, the output of the shaping amplifier T- is connected to ground which eliminates the No. 2 sweep. channel; When the switch is turned to terminal No. 3, the No. I sweep channel Ibecomes grounded. Thus, by setting'this switch to the previously mentioned positions, either of the two channels may be completely eliminated, thereby avoiding the above mentioned overlapping of the images. This is accomplished, however, at the expense of eliminating one of the transmitting-receiving channels which may not. necessarily be objectionable in connection with the desired purpose.

summarizing the operation of the radio locator illustrated in the Figs. 1, 6, and 7, it utilizes back-to-back antenna arrays for minimizing the o null effects of the antenna radiation patterns.

For more economical utilization of power, two transmitters using different frequencies are used, these transmitters being keyed simultaneously by a single modulator. The outputs of the transmitters are impressed simultaneously'on the two antennas which transmit the exploratory pulses 1n diametrically opposite directions, the antenna arrays IUE transmitting the early warning eX- ploratory pulses of lower frequency than the, exploratory pulses transmitted by the antenna III8.

17 The latter scans the space in the vicinity of the radio locator up to a height of 40 or 50 thousand feet. The antennas act as the transmittingreceivi-ng antennas, their outputs being impressed on the two receivers |38 and |40 respectively through the two duplexing circuits |34 and |36 when they act as receiving antennas. In order to avoid confusion of the images of different echoes on the screen of a single oscilloscope, and to prevent the reduction in the signal-to-noise ratio if the outputs of the two receivers were impressed simultaneously on al single video channel, the electronic switches |42, Md are inserted between the two receivers and the oscilloscope circuit, these switches blocking the output of one receiver and then the other in alternate succession. The synchronous operation of the electronic switches with the transmitter-receiver channels is obtained by controlling the sweep generating circuit of the oscilloscope by the pulses generated by the modulator and by using the rectangular waves generated in the sweep generator channels for rendering the electronic switches alternately conductive. Thus, only the output of one receiver is impressed on the linear amplifier |46 at any given time, and because the two saw-tooth waves impressed on the rotating deflection coils of the oscilloscope are of oppositie polarity, the cathode ray beam is first deected along one radius and then along the diametrically opposite radius as illustrated in Fig. 3. Proper synchronization of the sweep and the video channels results in the reproduction of all signals received by antenna |56 along one radial sweep trace, and all signals received by antenna |08 along thhe diametrically opposite sweep trace. Range markers are used for determining the range of the objects producing the echo signais, and the durations of the sweeps are adjusted so that the first marker occurs at the beginning of the sweeps. Circuits are also provided for reproducing the signals from only one receiver when the rotational speeds of the antennae are too high for the biradial sweep.

The advantages of the disclosed system should be apparent to those skilled in the art from the given disclosure. A PPI system possessing greater operating versatility has been disclosed. The early warning echoes as well as the short range echoes are reproduced on the screen of a single oscilloscope tube, thus enabling one operator to observe the entire eld scanned by the two antennas on one screen.

The invention has been illustrated and deu scribed in connection with a radio locator which uses two different transmitting frequencies for the reasons which have been fully outlined in the specification. It is obvious that the disclosed system will function equally well when the transmitters have the same frequencyv since none of the circuits which are claimed to be new depend on the transmitting frequency per se. The byradial sweep is obviously adapted and is so timed as to repro-duce the desired portions of the scanning lobes, but the timing circuits do not depend on the frequency of the transmitters. The use of two identical frequencies may prove advantageous when greater scanning rate of space is desirable than the scanning rate which can be achieved with the antennas possessing large mass and mounted on exceptionally high towers.

In describing the radio locator references were made throughout the specification to "echoes and echo signals, which ordinarily have .a

meaning in the art of' radio locators a reradiated energy, or that energy which is reradiated by the objects capable of reflecting or reradiating the radio waves when these objects find themselves in the path of the transmitted radio waves. There are now in use additional types of radio locating systems in which the objects are equipped with the transmitters which send signals in response to the reception of radio energy, the systems of the latter type being known as Identification Friend or Foe Systems, or IFF systems. rIlie radio locator disclosed in this specification may function equally well with either type of echo signals, and, as a consequence, the term echo as used herein is not to be restricted to signals which are reflected or passively reradiatecl by a body. This term is also used to signify any automatic response to a signal, e. g. that obtained yby means of a normally inoperative transmitter, located on said body, and which, when keyed by a pulse.- transmitted toward said body, automatically functions to send an answering pulse, either on the same frequency as said transmitted pulse or on a different frequency.,

It is believed that the construction and operation of my new PPI radio locator will be apparent` from the foregoing description. It should be understood nevertheless that while I have shown and described my invention in one preferred form, many changes and modifications may be made without departing from the spirit of my invention as sought to be defined in the following claims.

I claim:

l. In the method of determining the locations oiv objects by means of a pulse-echo radio system provided with first and second antennas, each of which has a principal lobe, the direction of the axis of the principal lobe of said first antenna being separated from the direction of the axis of the principal lobe of said second antenna by a given angle, and a single display screen for indicating said locations, the steps which include: generating a first sweep deiiection, pointing said first sweep deflection in a direction corresponding to the direction of the lobe axis of said first antenna by reproducing said firstv deflection along a first portion of said screen, displaying the echoes corresponding to the locations of all objects detected by said first antenna along said first deflection, generating a second sweep deflection, pointing said second deflection in a direction corresponding to the direction of the lobe axis of said second antenna by reproducing said second deflection along a second portion of said screen angularly displaced from said rst portion by said given angle, and displaying the echoes corresponding to the locations of all objects cletected by said second antenna along said second sweep deflection.

2. In the method of determining the locations of objects by means of a pulse-echo radio system provided with first and second directional antennas pointing in diametrically opposite directions with the axes of their lobes, said antennas being connected through two receiving channels to a common plan position indicator, those steps which include: generating a first radius vector in said indicator in the direction of the lobe axis of said first antenna, displaying the instantaneous locations of the objects detected by said first antenna along said first radius vector, generating a second radius vector in said indicator in the aca/,occ

Y 19 direction of the lobe axis of said second antenna, and displaying the instantaneous locations of the objects detected by said second antenna, along said second radius vector.

3; In the method of determining the location of objects as deiined in claim 2 which includes an additional step of generating said rstrand second vectors in alternate succession.

Li. In the method of determining the location of objects as defined in claim 2 which includes an additional step of generating said rst vector in terms of time so that it coincides with the reception of echoes only from the objects whose ranges are within the limits of the remote portion of the lobe of said nrst antenna.

5. In the method ofY determining locations of objects by means or" a radio pulse-echo object locating system having nrst and second directional antennas rotated in a horizontal plane and connected to a common plan position indicator, said indicator being capable of reproducing said locations in terms of range and azimuth along a polar coordinate system, the steps which include: generating a rst radius vector in said indicator, rotating said nrst vector in synchronism and in space-phase with the rotation of said iirst antenna for pointing said rst vector in the direction o the lobe axis or said first antenna, intensity modulating said rst vector by means of a first set of echo signals, received by said rst antenna, for reproducing along said first vector azimuth and range of objects producing said rst set of echo signals, generating a second radius vector in said indicator, rotating said second vector in' synchronism and in space-phase with the rotation of said second antenna for pointing said second vector in the direction of the lobe axis of said second antenna, and intensity modulating said second vector by means of a second set of echo signals, received by said second antenna, for reproducing along said second vector azimuth and range of objects producing said second set of echo signals.

6. In the method of determining locations of objects as deiined in claim 5 which includes the additional step of varying the time of occurrence of said second vector for selecting any desired portion of the range assigned to said second antenna.

7'. The method of measuring distance and azimuth of objects producing radio echoes in response to transmitted exploratory pulses in a form of radio energy by means of a single plan position indicator having a fluorescent screen, which includes the steps of radiating periodically a irst series of exploratory radio pulses in a first direction toward a rst set of reflecting objects, receiving a nrst series of echoes of said pulses from said iirst set of objects, generating, on said screen, a nrst sweep trace having a rst sweep rate along a direction corresponding to said rst direction to provide a first polar coordinate system, producing visual images of said first series of echoes along said rst polar coordinate system, the radial distance and the angular position of said images along said coordinates representing respectively the range and azimuth of said objects, radiating periodically a second series of exploratory radio pulses in a predetermined sequence with respect to said first series of pulses. in a second direction displaced from said first series by a given angle toward a second set oi reflecting objects, receiving a second series of echoes of said second pulses from said second set of objects, substantially simultaneously generating, on said screen, a second sweep trace having a second sweep rate along a direction displaced from the direction of said rst sweep trace by said given angle to provide a second polar coordinate system having common origin with said iirst polar coordinate system, producing a second set of visual images of said second series of echoes along said second polar coordinate system, the radial distance and the angular position of said second set of images along said second polar coordinate system representing the range and azimuth respectively of said second set of objects.

8. In the method oi determining range and azimuth of objects by means of a radio object locating system connected to a plan position indicator having an image-producing screen, said indicator reproducing locations of said objects on said screen along polar coordinate systems, the steps which include: simultaneously transmitting first and second directional exploratory pulses in two different directions and receiving first and second series of echoes in response to said pulses, generating a rst radius vector pointing in the direction of said iirst series of echoes, generating visual images of said rst series of echoes along said first vector while suppressing said second series of echoes, simultaneously transmitting third and fourth directional exploratory pulses in two different directions a predetermined time after the transmission of said rst and second pulses and receiving third and fourth series of echoes in response to said third and fourth pulses, generating a second raL ius vector pointing in the direction `oi said fourth series of echoes and generating visual images of said fourth series of echoes, on said screen, along said second radius vector having the same origin as said first vector while suppressing said third series of echoes.

9. In a biradial oscilloscope connected to two transmitters and two receivers, the method of timing oscilloscope circuits which includes the steps of generating keying pulses, simultaneously transmitting two exploratory signals in two different directions in response to each keying pulse, generating rst and second rectangular waves, said first wave being synchronized with the odd number of said pulses, and said second wave being synchronized with the even number of said pulses, generating a rst sweep wave in synchronism with said rst rectangular wave, generating a second sweep wave in synchronism with said second rectangular wave, and selecting the echoes of only one exploratory signal at any given time in alternate succession iirst by means of said first rectangular Wave, and then by means of said second rectangular wave, said iirst rectangular wave selecting echoes emanating from one direction and said second rectangular wave selecting echoes emanating from the other direction.

10. A radio object-locating system including a modulator; nrst and second transmitters simultaneously keyed by said modulator; an antenna system rotatable in azimuth and having a radiation pattern covering a given elevation angle, said antenna system including a rst directional antenna having a principal lobe which covers only a first portion of said given elevation angle and a second directional antenna having a principal lobe which covers substantially only the remaining portion of said elevation angle, said lobes being spaced in azimuth by a predetermined angle; first and second receivers connected respectively to said first and second antennas; a cathode ray tube 'indicator having a screen; and control means coupling said antenna system and said first and sec- 21 ond receivers to said indicator for presenting during spaced intervals a first composite display of the range and azimuth of signals received by said first antenna on said screen, and for presenting during intervals intermediate said spaced intervals a second composite display of the range and azimuth of signals received by said second antenna on said screen, said control means including means for alternately blocking said receivers and for simultaneously shifting the azimuth indications of therespective displays by an amount representative of said predetermined angle.

11. A radio object-locating system including a common modulator, first and second transmitters simultaneously keyed by said modulator, first and second directional antennas connected respectively to said first and second transmitters, said first and second antennas being arranged to have principal lobes lying in a vertical plane, the axis of the principal lobe of said first antenna having a relatively small angle of elevation and the axis of the principal lobe of said second antenna having a relatively large angle of elevation, first and second receivers connected respectively to said first and second antennas, and a' common plan position cathode ray tube indicator connected to said first and second receivers, said indicator having a screen for reproducing thereon signals from said receivers; which further includes a common vsupport for said antennas," said antennas being mounted on said support with the lobe axes of said antennas pointing in diametrically opposite directions, means for rotating said support, a rotating yoke for electromagnetically deecting the cathode-ray beam in said indicator, and electromechanical connections between said means and said yoke for rotating the magnetic axis of said yoke in synchronism and in space-phase with the lobe axes of said antennas.

12. A radio object-locating system including a common modulator, first and second transmitters simultaneously keyed by said modulator, nrst and second directional antennas connected respectively to said first and second transmitters, said first and second antennas being arranged to have principal lobes lying in a vertical plane, the axis of the principal lobe of said first antenna having a relatively small angle of elevation and the axis of the principal lobe of said second antenna having a relatively large angle of elevation, first and second receivers connected respectively to said first and second antennas, and a common plan position cathode ray tube indicator connected to said first and second receivers, said indicator having a screen for reproducing thereon signals from said receivers, wherein the principal lobes of said first and second antennas are separated in azimuth by a given angle, and which further includes a cathode-ray deflecting means connected to said indicator, and two sweep generating channels connected between said modulator and said deflecting means, one of said channels impressing a sweep voltage on said means deliecting the cathode ray beam of said indicator in the direction of the lobe axis of said first antenna, and the other channel impressing a sweep voltage on said means deecting said cathode ray beam in the direction of the lobe axis of said second antenna.

13. A radio object-locating system including a common modulator, first and second transmitters simultaneously keyed by said modulator, first and second directional antennas connected respectively to said first and second transmit-ters, said first and second antennas being arranged to have principal lobes lying in a vertical plane, the axis of the principal lobe of said first antenna having a relatively small angle of elevation andthe axis of the principal lobe of said second antenna having a relatively large angle of elevation, first and second receivers connected respectively to said rst and second antennas, and a common plan position cathode ray tube indicator connected to said first and second receivers, said indicator having a screen for reproducing thereon signals from said receivers, wherein the principal lobes of said first and second antennas are separated in azimuth by a given angle, and which further includes a cathode-ray deflecting means connected to said indicator, two sweep generating channels connected between said modulator and said defiecting means, said modulator so controlling said channels that one of said sweep channels deflects the cathode-ray beam of said indicator in the direction of the lobe axis of said first antenna, and the other channel deflects said beam in the direction of the lobe axis of said second antenna, and connections between one ofvsaid sweep channels and said rst receiver, and the other sweep channel and said second receiver, for blocking the output of one receiver ata time whereby the output of the first receiver is reproduced along one sweep, and the output of the second receiver is reproduced along the other sweep.

14. A radio object-locating system including a common modulator, first and second transmitters simultaneously keyed by said modulator, firstI and second directional antennas connected respectively to said first and second transmitters, said first and second antennas being arranged to have principal lobes lying in a vertical plane, the axis of the principal lobe of said rst antenna having a relatively small angle of elevation and the axis of the principal lobe of said second antenna having a relatively large angle of elevation, first and second receivers connected respectively to said first and second antennas, and a common plan position cathode ray tube indicator connected to said first and second receivers, said indicator having a screen for reproducing thereon signals from said receivers, wherein the principal lobes of said first and second antennas are separated in azimuth by a given angle, and which further includes a cathode ray deiiecting means connected to said indicator, two sweep generating channels connected between said modulator and said deiiecting means, said modulator so controlling said channels that one of said sweep channels deflects the cathode ray beam of said indicator in the direction of lobe axis of said first antenna, and the other channel deiiects said beam in the direction of the lobe axis of said second antenna, first and second electronic switches connected respectively to the outputs of said first and second receivers, a common video channel connected on its input side to said electronic switches and on its output side to said indicator, connections between one of said sweep generating channels and said first electronic switch, and the other sweep channel and said second electronic switch, for alternately blocking the outputs of said receivers whereby the output of the first receiver is reproduced along one sweep and the output of the second receiver is reproduced along the other sweep.

15. A radio object locating system as dened in claim 10 wherein said position indicator comprises a cathode ray beam generator and which further includes a range marker channel connected between said modulator and a mixer stage, said mixer stage being also connected on its input side to said first and second receivers and on its output'side to said indicator, said mixer stage inten.- sity modulating the cathode ray beam in said indicator for producing visual indications of the range: markers and of the echoes received by said rst and second receivers on the screen of said indicator.

16. A radio object locating system for determining range and azimuth of objects producing echoes in response to exploratory pulses including: a common modulator, first and second transmitters connected to said modulator, said transmitters being simultaneously keyed by said modulator, rst and second directional antennas connected respectively to said rst and second transmitters, said antennas being so mounted that the lobe axes of said antennas point in diametrically opposite directions whereby said antennas transmit exploratory pulses in two diametrically opposite directions, rst and second duplexing circuits, and rst and second receivers connected to said first and second antennas respectively, said rst receiver being capable of receiving echoes of the exploratory pulses transmitted by said first antenna, and said second receiver being capable `of receiving echoes of the exploratory pulses transmitted by said second antenna, rst and second sweep generating channels generating a series of positive and negative voltage waves in a predetermined relationship with respect to said exploratory pulses, a cathode ray tube, a rotatable electromagnetic deflection coil rotatively mounted with respect to said cathode ray tube, means for synchronously rotating said antennas and said coil, connections between said rst and second sweep channels and said coil whereby said sweep channels alternately impress upon said coil first the positive voltage wave and then the negative voltage wave for generating a rotating, bi-radial nections between said rst and second receivers and said cathode ray tube for intensity modulating the cathode ray in said tube so as to reproduce on the screen of said tube the output of the rst receiver along one sweep, and the output of the second receiver along the other sweep.

17. A system according to claim 10, wherein said control means further includes a rst sweep deflection channel providing said rst `display and a second sweep deection channel providing said second display, and said second channel includes means for variabiy delaying the relative occurrence in time of the output of said second channel relative to said first channel.

18. A system according to claim l0, further including a circuit, connected to be controlled by said modulator and having a connection to said indicator for control thereof, for generating range marker signals, for application to and for scaling of said indicator.

WILLIAM A. HUBER..

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Datev 2,189,549 Hershberger Feb. 6, 1940 2,227,598 Lyman et a1 Jan. 7, 1941 2,275,016 Koch Mar. 3, 1942 2,324,314 Michel July 13, 1943 2,395,966 Goldberg Mar. 5, 1946 2,430,307 Smith Nov. 4, 1947 2,449,976 Busignies Sept. 28, 1948 2,468,032 Busignies Apr. 26, 1949 2,515,178 Barchok July 18, 1950 

